Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/02—Sealings between relatively-stationary surfaces
  • F16J15/06—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces
  • F16J15/10—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing
  • F16J15/12—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing with metal reinforcement or covering
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/02—Sealings between relatively-stationary surfaces
  • F16J15/06—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces
  • F16J15/10—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing
  • F16J15/12—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing with metal reinforcement or covering
  • F16J15/121—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing with metal reinforcement or covering with metal reinforcement
  • F16J15/125—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing with metal reinforcement or covering with metal reinforcement generally perpendicular to the surfaces
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B30/00—Compositions for artificial stone, not containing binders
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L23/00—Flanged joints
  • F16L23/16—Flanged joints characterised by the sealing means
  • F16L23/18—Flanged joints characterised by the sealing means the sealing means being rings

Definitions

• the present invention is concerned with gaskets, in particular, with spirally wound gaskets having a sealing layer with enhanced properties which is based upon chemically exfoliated vermiculite.
• Exfoliated vermiculite is a known heat-resistant resilient material.
• Exfoliated vermiculite is conventionally formed by expanding mineral vermiculite using gas, this material being referred to herein as "gas-exfoliated vermiculite".
• the gas may be thermally generated, in which case the product is called “thermally-exfoliated vermiculite” (TEV) .
• TEV may be made by flash-heating mineral vermiculite to 750-1000°C, at which temperature the water (free and combined) in the ore vaporises rapidly and ionic repulsion forces apart the silicate sheets which form the raw material, so bringing about an expansion of 10-20 times perpendicular to the plane of the sheets.
• Gas-exfoliated vermiculite may also be made by treating raw vermiculite with a liquid chemical, eg hydrogen peroxide, that penetrates between the silicate sheets and subsequently evolves a gas, eg oxygen, to bring about exfoliation.
• a liquid chemical eg hydrogen peroxide
• CEV chemically-exfoliated vermiculite
• exfoliated vermiculite As a layer of a sheet gasket, eg an automotive exhaust gasket, and for other purposes.
• GB 2 193 953 B discloses forming sheet-like gaskets formed from particles of gas- exfoliated vermiculite. Because such particles do not cohere well, they are bound together by fine particles of CEV.
• CEV as a binder retains heat resistance and resilience, whereas the use of other inorganic binders could result in an incompressible structure.
• exfoliated vermiculite has excellent heat resistance and a high degree of resilience, . it has poor water resistance.
• such products were manufactured using CEV with a high water content at low solids content and considerable drying problems are encountered during production due to the tendency of CEV containing materials to form a surface skin which prevents the further escape of moisture.
• Spirally wound gaskets are well-known and are formed from a metal supporting strip, conventionally of steel, and a sealing strip formed from a resilient material, conventionally expanded graphite (also called exfoliated graphite) .
• the steel supporting strip is fed onto a mandrel.
• the steel supporting strip is welded either to itself to form a closed loop around the mandrel or, alternatively, is welded to an inner ring of the gasket which is itself mounted on the mandrel.
• the mandrel is then rotated to draw further supporting strip on to the mandrel to form a planar spiral.
• the sealing strip is drawn between the coils of the steel strip so that a spiral of the sealing strip is formed interposed between the coils of the supporting strip.
• the steel supporting strip is welded to itself to form a closed loop at the outside of the gasket and the gasket is removed from the mandrel .
• Such gaskets are utilised, for example, for forming seals between flanges at the ends of pipes.
• the supporting strip holds the sealing strip in position and the sealing strip forms a seal between the flanges and between the coils of the supporting strip.
• the sealing strip thereof must have sufficient strength and flexibility to enable it to be drawn into the spiral and formed into a gasket without breakage.
• WO98/53022 discloses the possibility of a spirally wound gasket having a sealing strip produced from CEV compositions with a carrier strip to prevent breakage of the resilient material which otherwise is deemed to be too brittle to allow formation of a spirally wound gasket. This technique has encountered problems with delamination of the carrier strip during slitting of the resilient layer. As a result, adhesive has . been applied in some instances to the resilient layer to prevent delamination from the carrier strip.
• a spirally wound gasket comprising a sealing strip wound into a spiral and a support strip wound into a spiral in such a manner that the spiral of the sealing strip is formed interposed between the coils of the supporting strip, the sealing strip comprising a resilient material, the resilient material comprising a CEV component in a proportion of at least 25% w/w of the sealing strip, the said CEV component being at least partially derived from dry CEV, wherein the sealing strip does not include a carrier strip.
• the resilient material also comprises a hydrolysis resistant polymer to improve the water resistance of said sealing strip, the proportion of the said polymer not exceeding 20% w/w of the sealing strip.
• the resilient material further comprises a plate like filler material, preferably, a milled filler material .
• the sealing strip has a small moisture content during spiral winding and, preferably, during removal from a forming sheet on which the sealing strips or layers are formed.
• the moisture content sufficiently reduces the brittleness of the strip or sufficiently increases the cohesion of the strip to allow said spiral winding and removal from the forming sheet without damage, such as splitting or tearing, to the strip.
• a spirally wound gasket of the present invention may provide conventional sealing between static parts.
• An example of the latter would be valve stem sealing.
• the proportion of CEV is at least 30% w/w of the sealing strip, more preferably at least 35% w/w of the sealing strip.
• the level of CEV falls within the range 25-80% w/w of the sealing strip, more typically, 30-75% w/w of the sealing strip, most typically 35-70% w/w of the . sealing strip.
• the proportion of the said polymer is less than 15% w/w of the sealing strip, more preferably, less than 10% w/w.
• a level of polymer less than 7.5% w/w, more especially preferred is a level of polymer in the range 1.0-7.5% w/w of the sealing strip.
• the chemically exfoliated vermiculite component of the present invention includes sufficient dry CEV, to provide a wet sealing layer dough with a reduced water content which is capable of being dried before substantial skinning has occurred.
• hydrolysis resistant polymer includes any suitable elastomer such as silicon and carbon based elastomeric polymers. Suitable polymers for use with the present invention include:-
• nitrile butadiene rubbers styrene butadiene rubbers, natural rubber, butyl rubber, siloxanes (particularly organosiloxanes such as dialkyl siloxanes) and ethylene- propyldiene monomer. Diene-based polymers are suitable because they are flexible and hydrolysis-resistant .
• the support strip may be made of any suitable support material with which the sealing layer may be wound to form the spirally wound gasket.
• Suitable support strip materials include stainless steel and special alloys such as Inconel and Hastoloy which may both be in the form of thin strips .
• a spirally wound gasket comprising a sealing strip wound into a spiral and a support strip wound into a spiral in such a manner that the spiral of the sealing strip is formed interposed between the coils of the supporting strip, the sealing strip comprising a resilient material, the resilient material comprising a CEV component in a proportion of at least 25% w/w of the sealing strip, the said CEV component being at least partially derived from dry CEV, wherein the sealing strip has a moisture level of between 3-20% w/w of the sealing strip resilient material during winding into the said gasket.
• the moisture level of the sealing strip during winding is between 2-10% w/w of the resilient material of the sealing strip, most preferably, 3-5% w/w.
• the sealing strip comprises 80% resilient material, more preferably 90% resilient material, most preferably, it consists substantially wholly of resilient material .
• the sealing strip in accordance with this aspect of the invention may or may not include a carrier strip.
• a sealing strip for a spirally wound gasket in accordance with the first or second aspect of the invention comprising the steps of:-
• the solids content of the wet sealing strip material prior to the drying step is in the range 20-70% w/w of the material.
• step (c) may be carried out after step (d) .
• the forming sheet is capable of withstanding drying temperatures applied to the wet sealing strip layer.
• the forming sheet may be stainless steel, a non-reactive polymer such as PTFE or other suitable material to which the layer does not stick.
• the solids content of the said sealing strip layer is in the range 25-60% w/w of the wet material, more preferably, 30-55% w/w of the wet material, most preferably, 35-50% w/w of the wet material.
• the CEV is mixed with a suitable plate-like filling agent such as thermally . exfoliated vermiculite (TEV) .
• TEV thermally . exfoliated vermiculite
• the filling agent is milled.
• the filling agent comprises less than 75% w/w of the sealing strip, more preferably, less than 70% w/w, most preferably, less than 65% w/w of the sealing strip.
• the water content of the partially dried layer during removal from the forming sheet is 3-20% w/w, more preferably 5-15%, most preferably 7-13%.
• the forming sheet may be a moving belt which may be continuous or not . In many cases the TEV content in the layer is less than 55% w/w.
• a further drying step may be carried out after removal of the sealing layer material from the forming layer.
• a wet sealing strip layer material dough in accordance with the present invention may be dried at temperatures between
• the material may also be allowed to dry around room temperature but it is envisaged that this will be difficult to commercialise.
• the wet sealing strip material is spread onto the forming sheet using a suitable spreading technique such as the application of a doctor blade. Calendering is also envisaged.
• the wet sealing strip material is in the form of a spreadable paste, preferably, a thin paste or a thick slurry consistency is utilised.
• the relative ratio of non-dry derived CEV to dry CEV in the dried sealing strip component is between 0.01:1 and 20:1, more preferably between 0.05:1 and 10:1, most preferably between 0.1:1 and 4:1.
• the resilient layer may also comprise particles of gas-exfoliated vermiculite, eg the strip may comprise particles of gas-exfoliated vermiculite bonded with the particles of CEV.
• the material used may be milled or otherwise reduced in particle size to a particle size of less than 50 ⁇ m, however, preferably, the particle size of at least a substantial proportion is more than 50 ⁇ m, preferably, 50-300 ⁇ m, more preferably 50-250 ⁇ m, most preferably 50-200 ⁇ m.
• Other possible additives include talc, mica and unexfoliated vermiculite.
• dry CEV CEV having a moisture content of less than 20% w/w, more preferably, less than 10% w/w, most preferably, less than 5% w/w.
• the CEV component in the wet material comprises a mixture of dried CEV and CEV available in a slurry form.
• a high solids content in the wet material assists reduction in skinning in the subsequent drying process whilst maintaining a high solids content in accordance with the invention.
• the dry CEV is prepared by a suitable drying technique .
• suitable drying techniques include: -
• any of the features or any preferred features of any aspect of the present invention may be combined with the first aspect and the reference to the first aspect in the method of the second aspect should be interpreted accordingly.
• the hydrolysis resistant polymer When utilised, the hydrolysis resistant polymer may be coupled to the vermiculite by a coupling agent.
• the layer is more water resistant than a material containing only vermiculite and a coupling agent and also more water resistant than a material containing only vermiculite and a polymer.
• the coupling agent may be a silane, eg a vinyl functional silane such as triethoxy vinyl silane
• the resilient material can comprise unexfoliated (intumescent) vermiculite which can, on heating of the gasket, eg in situ, form TEV to swell the resilient layer and, thus improve sealing.
• the resilient material may be bonded to the support strip by adhesive but it may be advantageous if it is mechanically bonded. Preferably, however, no adhesive is required.
• the support strip has end portions which are not bonded to the resilient material so that these end portions can be welded in the formation of the gasket .
• the plate-like filler may be selected from the group consisting of talc, molybdenum disulphide, hexagonal boron nitride, soapstone, pyrophyllite, milled thermally exfoliated vermiculite, mica, fluoromica, powdered graphite, glass flake, metal flake, ceramic flake, or kaolinites.
• a particularly preferred vermiculite material is one with a plate size substantially in the range 50-300 ⁇ for example FPSV available from W R Grace & Co. FPSV is a registered trade mark of W R Grace & Co.
• a plate-like filler has an average width of plates of at least three times the average thickness.
• the sealing layer may comprise 5-80%, eg 20-50%, by weight of the plate-like filler, preferably, 25-40% of the plate like filler is present in the dried sealing layer.
• a spirally wound gasket comprising a sealing strip based on exfoliated vermiculite, which strip comprises a polymeric binder, the strip providing improved sealing at temperatures at which the binder degrades.
• the sealing strip of any aspect of the present invention also comprises an intumescent material selected so that it expands at temperatures at which said hydrolysis resistant polymer degrades.
• the intumescent material expands to at least partially fill the void left by the binder, thereby helping to maintain sealing.
• the intumescent material is unexfoliated vermiculite because, after exfoliation, it has good heat resistance.
• partially exfoliated vermiculite ie vermiculite which has been exfoliated at a lower temperature than is normally required to fully exfoliate it.
• the unexfoliated or partially exfoliated vermiculite may be treated (by methods which are known per se) to reduce the temperature at which exfoliation occurs, eg the temperature can be reduced to as low as 160°C.
• Other possible intumescent materials include expandable graphite, sodium silicate, and perlite.
• the intumescent material may form up to 50% by weight of the layer but up to 20% is preferred.
• Figure 1 is a plan view of approximately half of a spiral wound gasket complete with half of its associated guide ring.
• Figure 2 is a cross-sectional view taken on line A-A of Figure 1. It is shown slightly enlarged for purposes of illustration.
• the gasket comprises a plurality of turns of a generally "V" cross-section metal strip.
• the innermost turns 12 and the outermost turns 13 are free from gasket material.
• the inner free end 14 is secured by spot welding to the adjacent underlying turn; the outer free end 15 is likewise secured to the adjacent underlying turn; also by spot welding.
• a plurality of turns 11 of a relatively soft gasket material 11, in accordance with the invention, are interleaved with the intermediate metal turns 10 during winding, as best seen in Figure 2.
• the overall spiral structure is thus a laminate sandwiched between plain metal turns .
• the radially outer rim of the spiral has a nose region 17 defined by the apex of the W V" cross section. This enables it to be “snapped into” an outer guide ring 16, the inner edge of which is provided with a machined or pressed groove 18 to receive it.
• the guide ring 16 is used to centre the complete gasket within the bolt circle of a flanged pipe joint, in the usual way, (not shown) .
• the bolts are tightened so that the opposed flanges apply pressure to the front and rear faces of the spiral wound annulus .
• This is then progressively compressed through deformation of the ⁇ , V" shaped cross-section until the pipe flanges seat onto the faces of the guide ring 16.
• the loading required to achieve this in a typical, conventional gasket is very high, as is discussed elsewhere in this specification.
• test sample in this case, 4" class 300 spiral wound gaskets
• elevated temperature sealing test 450°C
• the flange specification is ASTM A 182 Gr. Fll or F12
• the pipe specification is ASTM A 335 Pll
• Flanges are fastened together using 8 x ASTM A 193 Gr. B16 stud bolts, with ASTM A 194 Gr 4H nuts, lubricated with high temperature lubricant (molybdenum sulphide grease or similar) ,- tension is applied preferably using hydraulic bolt tensioners, the permitted range of final bolt stress being 210-350 N/mm 2 (the stress used in the tests described is 300 N/mm 2 ) .
• the test proceeds as follows : -
• results of the testing of the gaskets prepared from the resilient strip are summarised below: all are ASME B 16.20 4" Class 300 spirals with inner and outer rings using 316 stainless steel as the support strip for the spiral .
• the preferred construction is to use a winding pressure of generally 40 psi, with 4 inner and 5 outer winds of steel.
• Polymer-free strip was tested and, to improve resistance to water, polymer containing strip having 5% NBR binder (as solution) was also tested as per the formulation in Method A.
• Sample 1 Polymer free filler; 3 inner winds and 4 outer winds steel; wound at 40 psi.
• Sample 7 As Sample 6, wound at 20 psi
• Sample 8 As Sample 6, with filler dried but not cured*.
• Sample 9 As Sample 5 with latex based filler (2%%) on 0.05mm steel. (Test performed at 200 psi and 450°C. When tested, at 500 psi and 450°C, the pressure drop was an unacceptable 200 psi ( ⁇ 14 bar) after hour of first dwell at 450°C) .
• Samples 5-7 have filler cured before winding (180°C/1 hour) .
• the paste is prepared as follows (Z-Blade mixer):- Grace Microlite HTS Dispersion 18.07kg
• NB - FPSV is fine-milled TEV.
• Latex based paste also containing 5% by dry weight of NBR incorporated in the form of water-based latex (40% solids) so that 2.50kg of latex is equivalent to the 6.10kg of rubber solution (sample 5) .
• the paste needs to be applied in the form of a thick slurry ( "buttercream" consistency) and is prepared by thinning the paste formulations which are described below by adding water. Take 2 parts of paste (up to 2kg) break up into handful sized lumps in a clean container and pour over 1 part of water (by weight), stir to a consistent texture. The preferred formulation for the paste (without the additional water) is described below.
• An even coat of paste which dries to approximately 0.6mm thickness is applied to a forming sheet thickness of up to 0.1mm using a doctor blade set to about 2mm.
• the paste may be allowed to dry at room temperature, whereupon the forming sheet is then removed to leave a film of paste.
• the paste layer is then dried further, at 120°C, the film in the form of a strip 124mm wide by up to 5m long is then slit and wound. Typically the film is passed through crimping rollers beforehand to make it more flexible.
• the paste may be applied by using a "double" blade, so that one applies a coarse coat of the slurry, and the second smooths it out, regulating the thickness and removing any air bubbles at the same time.
• the possibility is envisaged of driving the forming sheet, so that it moves at a constant rate through the coating device.
• the CEV used was W R Grace's HTS dispersion which is approximately 15% solids.
• the dry CEV used was W R Grace's "Microlite Powder” .
• the FPSV was also obtained from W R Grace.
• the rubber used in these examples was either nitrile rubber N36C80 from Zeon.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Gasket Seals (AREA)
• Sealing Material Composition (AREA)

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• 2000
  • 2000-01-14 GB GBGB0000712.0A patent/GB0000712D0/en not_active Ceased
• 2001
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• 2004
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